In order to ensure that the database accurately reflects the data reported in the CRF, a double data entry procedure (data entered by different staff in two separate data files) will be used. In addition to an electronic comparison of these two data files a validation of the data will check ranges, consistency and plausibility. Unclear data will undergo a data cleaning process ("queries"). Any changes applied to data in the database during data cleaning will be recorded in a special log file. The database will be frozen on completion of data cleaning.